1. Field of the Invention
This invention relates to a process for preparing organic hydroperoxides by selectively converting aryl alkyl hydrocarbons in the presence of an oxygen-containing gas and certain tetranuclear manganese complexes as a catalyst. Such conversion is carried out without decomposition to any appreciable extent of the resulting organic hydroperoxides.
2. Description of the Prior Art
The production of organic hydroperoxides from aryl alkyl hydrocarbons in the presence of various transition metal salt complexes has been described in the literature (see, for example, U.S. Pat. No. 2,954,405 concerning the production of organic hydroperoxides by autooxidation of hydrocarbons in the presence of molecular oxygen and metal phthalocyanines as catalysts). In '405, certain phthalocyanines were found to catalyze autooxidation without significant decomposition of the organic hydroperoxides to undesirable side products, as was the case in many previous processes. However, U.S. Pat No. 2,954,405 is not the same catalyst complex. Further, when the '405 catalyst contains manganese, the reaction does, in fact, produce undesirable by-products. Therefore, it does not teach nor disclose the process of the present invention. Similarly, U.S. Pat. No. 4,013,725 discloses a process for preparing hydroperoxides in a homogeneous system by autooxidizing secondary alkyl group-substituted methylbenzenes in the presence of water, a base, an oxygen containing gas, and a water- soluble chelate compound in which multidentate ligands are coordinated to at least one metal from the class of cobalt, nickel, manganese, copper, and iron. The multidentate ligand may include nitrogen containing polycarboxylic acids. The process may be distinguished from that of the present invention on several grounds. First, while both the organic ligand used in the process of the '725 patent and the present invention are amino acids and, hence, contain both amino and carboxyl groups, the process of the present invention uses a catalyst that contains an additional essential alkoxide group, which is not taught nor disclosed in the process of the '725 patent. Second, the process of the '725 patent requires the presence of significant amounts of water to dissolve the catalyst and to carry out the hydroperoxidation process. The present invention adds the catalyst in situ: no water is required. Finally, the '725 patent requires continuous adjustment of the pH of the solution to a value between 5 and 7.5 using alkali salts. No additional reagents are required to adjust the pH in the process of the present invention.
In U.S. Pat. No. 5,025,101, applicants taught and claimed the tetranuclear manganese complexes and their method of preparation, which complexes are used as the catalyst in the process of the present invention. In '101, applicants found that the complexes were useful as hydrogen peroxide decomposers. Applicants have now discovered the unexpected result that these complexes are effective in the process of selectively producing organic hydroperoxides from aryl alkyl hydrocarbons, but that they do not catalyze the decomposition of those organic hydroperoxides. The result is unexpected since transition metal ions are generally known to decompose hydroperoxides catalytically; thus, the expectation is that a metal complex that vigorously decomposes them will also decompose organic hydroperoxides.